抽象的な

Vegetation Changes along a Geomorphological Gradient under Arid Bioclimate in North

Mohamed Chaieba, Franck Torre and Saad Ouled Dhaou

In north Africa the floristic richness and diversity are mainly due to its precarious bioclimate, geomorphology, soil and human activities. Ecosystem components have been formed and developed under these very different ecological conditions. Our study was conducted in a part of north Africa to analyze major relationships among vegetation distribution and landform in an protected ecosystems, case of Bou Hedma National Park (BHNP) in southern Tunisia.

Multivariate analysis of 200 vegetation plots along geomorphological gradient in the BHNP, allowed us to classify complex mosaics of landforms and plant communities. By assessing plant community distribution in the context of the different landform units and geomorphic processes, represented in detailed geomorphological schema, a sequence of landform-vegetation units and soil properties were identified. A total of fourty seven perennial species in four landform types were analyzed using correspondence analysis. Multivariate analysis identified five community types defined by physical soil properties and geomorphological conditions (A, B, C, D1 and D2).

Our results showed that the highest total number of species is recorded in the Glacis (20), whereas the lowest species numbers are recorded in the Mountain (13) and in the silty plain (15). Community C appears to be rather different, with 5 characteristic species (Tricholaena teneriffae L., Raetama retam Forssk, Deverra chloranthus Bent, Periploca angustifolia Labill. and Rhus tripartita Ucria). We can be also noted that organic matter, phosphorus and nitrogen attain their highest levels in the group of wadis and sandy plain, the low level of nutrients and low sand content on the glacis and mountain.